Virtual Sensor for Calibration of Thermal Models of Machine Tools

Machine tools are important parts of high-complex industrial manufacturing. Thus, the end product quality strictly depends on the accuracy of these machines, but they are prone to deformation caused by their own heat. The deformation needs to be compensated in order to assure accurate production. So an adequate model of the high-dimensional thermal deformation process must be created and parameters of this model must be evaluated. Unfortunately, such parameters are often unknown and cannot be calculated a priori. Parameter identification during real experiments is not an option for these models because of its high engineering and machine time effort. The installation of additional sensors to measure these parameters directly is uneconomical. Instead, an effective calibration of thermal models can be reached by combining real and virtual measurements on a machine tool during its real operation, without additional sensors installation. In this paper, a new approach for thermal model calibration is presented. The expected results are very promising and can be recommended as an effective solution for this class of problems. 1. Introduction In high-complex industrial manufacturing processes the end-product quality depends strictly on the accuracy of relevant machine tools. When a machine tool operates, heat is produced by motors, points of friction like gears and bearings, and so forth. The heat spreads through the other parts of the machine and leads (via thermal expansion) to deformation of the machine tool. This deformation is often a reason of insufficient quality of produced goods. In particular, the accuracy of the “tool center point” (TCP) estimation is important for exactness of production. Since it is often not possible or too expensive to avoid this deformation (by constructional solutions or by additional cooling), the alternative solution should be aware of the deformation and compensate it by adjusting the tool or work piece position. This adjustment can occur inside a suitable machine tool control system (e.g., “computer numerical control” (CNC)). Unfortunately, the deformation value cannot usually be measured during production directly (i.e., online) because of economic and technical reasons. So an adequate model of thermal deformations in a machine tool can be used for the prediction of the TCP deviation. After the current TCP deviation is estimated, an appropriate adjustment will occur inside the CNC. In [1] an extended state-of-the-art review of thermal deformation modeling for complex physical systems is described. In this review, two